Mercury tracer model simulations are performed to support the analysis of the total gas phase mercury (TGM) observations on 15 flights of the NSF/NCAR C-130 aircraft during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) campaign conducted during April 2001. Ninety-seven percent of the observed mercury concentrations are greater than 1.2 ng/m3. The mean value of the observations is 1.9 ng/m3. No simple relationships between Hg-CO and Hg-total sulfur are found; however, strong correlations are observed in individual flight segments. Backward trajectory analysis is used to help characterize regional of Hg/CO ratios, and these are compared with emission-based ratios from the various sectors. Model predictions using new Hg emission estimates are presented and compared to the observations. Under the condition of a mercury background level of 1.2 ng/m3 the tracer model underestimates the observations when the flights were over the Yellow Sea but is consistent with the observations when the flights were over the Japan Sea. Further analysis suggests that Hg emissions are underestimated in north central China and the eastern coastal areas of China. Model sensitivity studies indicate that the emissions of China may be underestimated by 80--200%.